Mobile communications networks are in the process of offering increasingly sophisticated capabilities associated with the motion and/or position location sensing of a mobile device. New software applications, such as, for example, those related to personal productivity, collaborative communications, social networking, and/or data acquisition, may utilize motion and/or position sensors to provide new features and services to consumers. Moreover, some regulatory requirements of various jurisdictions may require a network operator to report the location of a mobile device when the mobile device places a call to an emergency service, such as a 911 call in the United States.
Such motion and/or position determination capabilities have conventionally been provided using digital cellular positioning techniques and/or Satellite Positioning Systems (SPS). Additionally, with the increasing proliferation of miniaturized motion sensors (e.g., simple switches, accelerometers, angle sensors, etc), such on-board devices may be used to provide relative position, velocity, acceleration, and/or orientation information.
In conventional digital cellular networks, position location capability can be provided by various time and/or phase measurement techniques. For example, in CDMA networks, one position determination approach used is Advanced Forward Link Trilateration (AFLT). Using AFLT, a mobile device may compute its position from phase measurements of pilot signals transmitted from a plurality of base stations. Improvements to AFLT have been realized by utilizing hybrid position location techniques, where the mobile station may employ an SPS receiver that can provide position information independent of the information derived from the signals transmitted by the base stations. Moreover, position accuracy can be improved by combining measurements derived from both SPS and AFLT systems using conventional techniques.
In conventional digital cellular networks, position location capability can be provided by various time and/or phase measurement techniques. For example, in CDMA networks, one position determination approach used is Advanced Forward Link Trilateration (AFLT). Using AFLT, a mobile device may compute its position from phase measurements of pilot signals transmitted from a plurality of base stations. Improvements to AFLT have been realized by utilizing hybrid position location techniques, where the mobile station may employ an SPS receiver that can provide position information independent of the information derived from the signals transmitted by the base stations. Moreover, position accuracy can be improved by combining measurements derived from both SPS and AFLT systems using conventional techniques.
Furthermore, navigation devices often support popular and increasingly important SPS wireless technologies which may include, for example, the Global Positioning System (GPS) and/or a Global Navigation Satellite System (GNSS). Navigation devices supporting SPS may obtain navigation signals as wireless transmissions received from one or more transmitter equipped satellites that may be used to estimate geographic position and heading. Some navigation devices may additionally or alternatively obtain navigation signals as wireless transmissions received from terrestrial based transmitters to estimate geographic position and heading and/or include one or more inertial sensors (e.g., accelerometers, gyroscopes, etc.) that reside on-board the navigation device to measure an inertial state of the navigation device. Inertial measurements obtained from these inertial sensors may be used in combination with or independent of navigation signals received from satellite and/or terrestrial based transmitters to provide estimates of geographic position and heading.
Several issues arise when combining a GNSS navigation system with sensor based navigation in a vehicle. One such issue lies with the importance of heading in the navigation filter. With a vehicle model, vehicle heading must be initialized and maintained to receive the full benefit of the sensors. Heading initialization can be difficult in low speed and/or bad GNSS environments.
After a heading is initialized, a gyroscope device that is sensitive in the vertical direction and odometry are the sensors available for dead reckoning on the vehicle. This allows for dead reckoning by assuming the vehicle roll and pitch are both close to zero (i.e., dead reckoning in a two-dimensional sense). Given that GNSS data and reality contain a vertical dimension to estimate, there exists a necessity to account for this in the navigation system.
A second concern during navigation is the lever arm between the odometry in the vehicle and the GNSS receiver present on the mobile device. The effect of an unknown lever arm is seen when the vehicle is executing a turn. Treating the receiver data as if there is no lever arm in this case leads to carrier phase based pseudo-range rates to significantly disagree with velocity based on dead reckoning. This unknown quantity must be accounted for when dead reckoning so as to allow GNSS measurements to agree.